The correct option is **C. Liquid-in-glass thermometer**. ### Explanation of the Correct Answer A liquid-in-glass thermometer is a device that measures temperature based on the principle of thermal expansion of a liquid, typically mercury or colored alcohol. Here’s how it works: 1. **Basic Principle**: When a liquid is heated, it expands. This expansion causes the liquid to rise in a narrow glass tube. The height of the liquid column corresponds to the temperature, which can be read on a calibrated scale printed on the glass. 2. **Components**: The thermometer consists of a glass bulb filled with either mercury or alcohol, connected to a narrow capillary tube. The bulb is usually sealed at the top, creating a vacuum above the liquid. 3. **Calibration**: The thermometer is calibrated to a specific scale (Celsius, Fahrenheit, or Kelvin). The scale is marked on the glass tube, allowing users to read the temperature directly from the height of the liquid column. 4. **Advantages**: Liquid-in-glass thermometers are simple, reliable, and can measure a wide range of temperatures. Mercury thermometers are particularly known for their accuracy, while alcohol thermometers are often used in lower temperature ranges because alcohol does not freeze as easily as mercury. ### Why Other Options Are Incorrect - **A. Bimetallic thermometer**: This type of thermometer uses two different metals that expand at different rates when heated. These metals are bonded together, and as they expand, they bend, moving a pointer on a dial to indicate temperature. While effective, it does not use liquid expansion, making it different from the liquid-in-glass thermometer. - **B. Digital thermometer**: Digital thermometers use electronic sensors to measure temperature. They convert the temperature reading into a digital format, which is displayed on a screen. This type does not rely on the physical expansion of a liquid, so it is not the correct answer. - **D. Infrared thermometer**: Infrared thermometers measure temperature from a distance by detecting the infrared radiation emitted by an object. They do not use any liquid or physical contact to measure temperature, making them fundamentally different from liquid-in-glass thermometers. ### Summary of Key Points - **Liquid-in-glass thermometers** measure temperature through the expansion of a liquid (mercury or alcohol) in a glass tube. - They are calibrated to a specific temperature scale, allowing for direct reading of temperature. - Other types of thermometers (bimetallic, digital, infrared) operate on different principles and do not use liquid expansion. - Understanding the working principles of different thermometers is crucial for selecting the appropriate one for specific applications. This thorough understanding of the liquid-in-glass thermometer and its comparison with other types will help you in your studies and exams.